1. Field of the Invention
This invention relates to a method and apparatus for monitoring the properties of flames in high pressure combustors and gasifiers in real time. More particularly, this invention relates to a sensor for real-time monitoring of flame properties using fiber optic spectroscopic digital imaging. Although intended for use in connection with pressurized combustors and gasifiers, the method and apparatus of this invention may be employed in any combustion apparatus in which slagging occurs or in which the environment of the combustion process is particle- and/or particulate-laden, i.e. a “dirty” or “dusty” environment, including processes at about atmospheric pressure.
2. Description of Related Art
Real-time monitoring of flame properties in high pressure combustors and gasifiers is increasingly important for providing stability, control, and optimization of combustion processes. Present control methods are mostly limited to the measurement of global system parameters such as output product compositions and emission levels or to the measurement of parameters which provide only limited information regarding the overall processes. Measurements performed inside the flame zone using thermocouples or optical pyrometers generally provide only point or line-of-sight information that is insufficient for characterizing the overall combustor performance. See, for example, U.S. Pat. No. 4,400,097 to Koschnitzke et al. which teaches a system for measuring temperatures in a high pressure reactor using an optical pyrometer which is in optical communication with a measuring duct which may be disposed in the reactor wall and is in optical communication with the reactor interior.
The use of fiber optics in a flame analyzer for analyzing one or more properties of a flame is known. U.S. Pat. No. 4,644,173 to Jeffers teaches a flame analyzer comprising a fiber optic array having a plurality of optic fibers, each of which has a light receiving end lying in a line and facing a flame. Each fiber of the array collects light from a specific location in the flame along a line extending parallel to the flame and burner axis or extending perpendicular to the flame axis. The light received by the fiber optic array is provided as a sheet of light to a monochromator which spreads the light into its component wavelengths. A pair of spaced apart arrays of light detectors is then utilized to measure the light at two discrete wave lengths. The detection produces signals that can be analyzed to generate temperature and particles distribution values for the flame across its length or width.
U.S. Pat. No. 5,828,797 to Minnott et al. teaches a fiber optic linked flame sensor for continuous optical monitoring of the combustion process within the combustion chamber of a gas turbine engine, which sensor includes a high temperature optical probe, a fiber optic cable, and an electro-optics module. The high temperature probe is mounted on the engine skin and sighted in a manner so as to view the combustion process taking place at its origin just aft of the fuel nozzle. It will be appreciated that the view of this probe is limited to a very small portion of the combustion process.
High pressure combustion and gasification processes would benefit enormously from novel non-intrusive imaging monitoring sensors that provide spatially-resolved information on flame properties. However, such processes present several challenges to measurements inside the combustor or gasification reactor vessels. For example, to effect temperature measurements within gasification reactor vessels using conventional means requires the insertion of a temperature probe into the gasifier. However, slag on the walls of the gasifier must be traversed by the probe if measurements are to be made within the interior of the gasifier. In addition, reliability of the measurements is difficult to obtain due to the harsh environment inside the gasifier in the form of dust particles, etc., which tend to obscure the temperature measuring device such that measurements therein may not be obtainable at all or, if obtainable, may be distorted. U.S. Pat. No. 5,372,618 to Andrus, Jr. teaches a temperature measuring device which includes a slag shield mounted on the gasifier so that a portion of the slag shield extends into the gasifier through an opening with which the gasifier is provided for this purpose, and a temperature measuring instrument in the form of a radiation thermometer or optical pyrometer mounted in supported relation within the slag shield so that line-of-sight exists from the temperature measuring instrument into the interior of the gasifier at a point of interest for temperature measurement. The temperature measuring instrument is provided with cooling means for cooling at least the portion of the slag shield extending into the interior of the gasifier and is provided with purge gas means for supplying a flow of purge gas in the area around the temperature measuring instrument to purge particulate matter therefrom and, thus, ensure that the line-of-sight between the temperature measuring instrument and the interior of the gasifier remains unobscured.